(a) Field of the Invention
The present invention relates to a group of winding electrodes. More particularly, is relates to a group of winding electrodes removing an unnecessary separator in the center of cylindrical nickel-hydrogen cell to increase the inner space and the electrolyte solution of the cell, and to have higher capacity and lower pressure of a can while producing a gas.
(b) Description of the Related Arts
A group of winding electrodes such as a cylindrical cell and a condenser has a separator to prevent a short-circuit of the cathode and the anode. The present invention relates to a technology of a group of winding electrodes having cathode, anode and separator. A cylindrical cell, especially a cylindrical nickel-hydrogen cell, is described as an example.
More and more portable electronic devices such as a camera, a camcorder, a portable CDP, a radio, a cassette, a notebook computer, a pager and a cellular phone, etc. require a cell having higher capacity and longer durability.
In general, a cell is a device that converts chemical energy into electric energy by means of contact potential difference and it has many kinds of thereof. Electrochemical cells and batteries are technologically identified as a nonchargeable primary cell or a rechargeable secondary cell or a fuel cell that converts combustion heat into electric energy or a solar cell that converts light energy into electric energy. Electrochemical cells and batteries are classified by the composition of electrolyte and shape of the cells and batteries. The composition of electrolyte and shape are alkaline, solid or nonaqueous cells and cylindrical, button or coin types respectively.
In these kinds of cells, a cylindrical cell (jelly-roll type) discharges current and is composed of a cathode, an anode, a separator to prevent a short-circuit of the cathode and the anode, electrolyte, a positive terminal, and a negative terminal. To describe specifically, the structure of a nickel-hydrogen cell is illustrated in FIG. 5. The cylindrical nickel-hydrogen cell is composed of a cathode (13) coated with Ni(OH).sub.2 as a positive active material, an anode (15) of hydrogenated alloy coated with a negative active material which is mainly composed of LaNi.sub.5, MmNi.sub.5, Ti--Fe or Ti--Ni alloy, a separator (17) which is made of a nonwoven fabric and a cellophane tape to prevent a short-circuit of the cathode (13) and the anode (15), a cap (19) as a positive terminal, and a case (11) as a negative terminal and packaging equipment, and besides a gasket (21), a safety vent (23), a cover plate (25), an insulating tube (27),and an insulating plate (29).
The process for producing a cylindrical nickel-hydrogen cell is as follows. First, cathode is manufactured by coating a slurry of a positive active material, drying, and rolling on a metallic support, and then an anode is manufactured by coating a slurry of a negative active material, drying, and rolling on a metallic support. After that, a separator is laid between the cathode and the anode, and is wound. In this wound assembly of electrodes and the separator is inserted into a can. After that, an electrolyte is poured into the can and a cap assembly is mounted in the mouth of the upper part.
A detailed description about the charge and the discharge reaction of the cylindrical nickel-hydrogen cell manufactured according to the above method is as follows.
A hydrogenated alloy is used as a negative active material, nickel hydroxide is used as a positive active material and potassium hydroxide(KOH) aqueous solution is used as an electrolyte. The hydrogenated alloy store hydrogen ions produced by cleavage of water in the electrolyte during the charging process, and releases hydrogen ions into the electrolyte during the discharging process. The charge and discharge reactions are as follows. ##STR1##
In the above reactions, M is a hydrogenated alloy that can absorb and emit hydrogen ions, identified as an AB.sub.5 group that is made of rare earth elements or an AB.sub.2 group that is made of Ti, Zr, V, etc. According to the above reaction, a cell performs a charge and discharge more than hundreds of times.
The process for producing the cylindrical nickel-hydrogen cell comprises locating the cathode (13) and the anode (15) in the opposite side of the separator (17) and winding the separator (17) using a mandrel as shown in FIG. 1. FIG. 2 is a cross-sectional view of a cylindrical cell inserted the plates and the separator therein. As shown in FIG. 3, when winding the cathode (13) and the anode (15), the portion which the separator is not piled on the plates, is overlapped in the center of the cell. The portion cannot make a role of the separator (17), which prevents short-circuit of the cathode (13) and the anode(15), to be unnecessary. The separator (17) is occupied the space, in which the electrolyte solution contains, therefore the problems that the electrolyte solution amount in the cell is decreased to have lower cell capability and the shorter durability.